Hi Glenn....
Before emissions control, fuel tank pressures/fumes were vented overboard
(or "equalized") via a vented fuel cap.
With the advent of emissions controls, the
fuel system became part of the "closed loop" crankcase breathing system via the
absorption cannister you speak of which
was mounted in the right rear inner
fenderwell within the trunk. This fed
these fumes/pressures into the carbon
cannister in the engine compartment, from
which flowed inbound air into the crankcase through a "graduated orifice"
in the valve cover. This crankcase air was
then fed into the intake manifold or
combustion process via either a PCV valve, or "graduated orifices" built into
the carb(s).
Cap'n Bob
Emissionless Frog
(again) "graduated orifices" contained
within the carb(s)
|